Resin additives such as phenolic antioxidants, ultraviolet absorbers and hindered amine compounds are known to inhibit deterioration of organic matters such as synthetic resins caused by light and/or heat.
In general, a compound to be used as a resin additive is preferably one which has a high melting point and shows limited plasticization of a resin and evaporation from a resin, such as tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxymethyl)methane or tris(2,4-di-tert-butylphenyl)phosphite. However, an additive having an excessively high molecular weight cannot move in a resin, so that its stabilizing effect tends to be small.
Meanwhile, low-melting-point compounds such as stearyl(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and bis(2,2,6,6-tetramethylpiperidyl)sebacate have a relatively low molecular weight and thus exhibit excellent initial stabilizing effect; however, since they readily evaporate from a resin, their long-term stabilizing effect is poor. In addition, those compounds that are in the liquid, viscous or powder form generate large aggregates during storage due to caking and are thus poor in the ease of handling; therefore, in order to improve the ease of handling, these compounds are required to be masterbatched.
However, when an ordinary hindered amine compound or benzoate compounds is used in a polyolefin resin, it exhibits low compatibility with the resin; therefore, in the preparation of a masterbatch comprising such a compound at a high concentration, there is a problem that a condition where the hindered amine compound or benzoate compound bleeds out to the pellet surface and the resulting pellets adhere to each other to form an aggregate is generated, that is, a problem of agglomeration. Particularly, in cases where a hindered amine compound having a low melting point (for example, a melting point of not higher than 80° C.) is used, it is melted and bleeds out under a high temperature of summertime or the like. Such a hindered amine compound is also solidified when cooled to cause solidification of masterbatch pellet; therefore, there is a drawback in terms of the storage stability (agglomeration resistance).
For example, those hindered amine compounds that are obtained by a reaction between 2,2,6,6-tetramethyl piperidinol and fatty acid exhibit excellent light stability effect; however, they are likely to be in the form of liquid at a low molecular weight. Therefore, when such hindered amine compounds are masterbatched with a resin so as to improve the ease of handling, there is a problem that the additive tends to bleed out to the surface of the masterbatched resin composition to show adhesive property.
As a method for improving the surface tackiness caused by bleeding of an additive component in such resin additive masterbatches, there have been proposed, for example, a method in which tackiness is suppressed by masterbatching with an oil-absorbing polymer (Patent Document 1), a microencapsulation method (Patent Document 2) and a method in which tackiness is suppressed by masterbatching with an organic acid metal salt (Patent Document 3). However, when an oil-absorbing polymer is used, it remains in the resulting resin composition. In addition, for example, microencapsulation is costly. Therefore, none of these proposed methods is satisfactory.